Question

If the first term of an A.P. is 2 and common difference is 4, then the sum of its 40 terms is
(a) 3200
(b) 1600
(c) 200
(d) 2800

Answer 1

Answer:

The sum of its 40 terms is 3200.

Among the given options option (a) 3200  is a correct answer.

Step-by-step explanation:

Given :

First term,(a) = 2 , common Difference ,d = 4 , n = 40

By using the formula ,Sum of nth terms , Sn = n/2 [2a + (n – 1) d]

S40 = 40/2 [2 x 2 + (40 - 1) 4]

S40 = 20 [4 + 39 × 4]

S40 = 20 (4 + 156)

S40 = 20 × 160

S40 = 3200

Hence, the sum of its 40 terms is 3200.

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Answer 2

Answer

(a) 3200

Explanation

Given

In an A.P.

First term (a) = 12

common diff. (d) = 4

To Find

Sum of first 40 terms

Solution

We have

a = 2, d = 4, n = 40

From the identity

$\star \boxed{S_{n}= \dfrac{n}{2}[2a+(n-1)d]}$

$S_{40}= \dfrac{40}{2}[2(2)+(40-1)4]$

$S_{40}= 20[4+(39)4]$

$S_{40}= 20[4+156]$

$S_{40}= 20[160]$

$S_{40}= 3200$

Hence, sum of the 40 terms = 3200